Silurian Trace Fossil Burrows in Dingle

Chondrites are trace fossils or ichnofossils. They are small branching burrows or tunnels that were made while the sediments were still soft and have subsequently become preserved in the hardened strata. There is a great deal of uncertainty about which organisms created the burrows because no animal has ever been found within them – but they may have been some kind of small marine worm. There is evidence to support the idea that the burrows were formed in sediments with reduced oxygen or none at all.

The trace fossil Chondrites, a highly branched burrow system of unknown endobenthic deposit feeders, occurs in all types of sediment, including those deposited under anaerobic conditions. In some cases, such as the Jurassic Posidonienschiefer Formation of Germany, Chondrites occurs in black, laminated, carbonaceous sediment that was deposited in chemically reducing conditions. In other cases, such as numerous oxic clastic and carbonate units throughout the geologic column, Chondrites typically represents the last trace fossil in a biotutbation sequence. This indicates that the burrow system was produced deep within the sediment in the anaerobic zone below the surficial oxidized zone that was characterized by freely circulating and oxidizing pore waters.

The Chondrites shown in these pictures occurred in Silurian rocks of the Dunquin Group on the Dingle Peninsula in western Ireland. Some were found in beach stones at the northern end of Smerwick Harbour, however, the majority were photographed in Clogher Bay on large boulders and in bedrock.